Water pumps as used in a marine engine, have been traditionally produced by sand casting techniques. As a pump housing contains a number of chambers as well as openings for water flow and the drive connection, a complex sand casting pattern is required which includes a number of separate cores and core supports, thus resulting in a substantial cost for the cast pump housing.
Evaporable or lost foam casting processes have been used in the past to cast a variety of metal parts, particularly parts having thin wall sections or complex contours. With evaporable foam casting procedures, cores and core supports are eliminated, and the evaporable foam procedure provides smooth finished castings more attractive in appearance than those produced by sand casting.
In a typical evaporable foam casting process, a pattern is formed of a polymeric foam material, such as polystyrene or polymethylmethacrylate, having a shape or contour corresponding to the part to be cast. The polymeric foam pattern is placed in a mold and an unbonded flowable material, such as sand, is introduced into the mold surrounding the pattern and filling the cavities within the pattern. A molten metal is fed into the mold via a sprue and the heat of the metal will vaporize the polymeric foam material with the vapor being trapped within the interstices of the sand, while the molten metal will fill the void created by vaporization of the foam to provide a solidified metal casting corresponding in shape to the foam pattern.